Structural Diagnostics : Assessing Fire Damage
Dudley Engineering is experienced with assessing foundations which have been exposed to fire damage. When assessing a foundation exposed to a fire we look for the following visual cues:
- scorch marks
- Smoke stains and scorch marks are typically good indicators of areas that were exposed to high heat and require further evaluation (see sounding hammer below)
- Concrete exposed to high heat and then subsequently doused with water as is typical in a normal structural fire, can lead to drastic temperature changes and hence quick expansion and contraction of concrete leading to cracks. Consider placing a glass in the freezer and then subsequently removing it and running hot water over it, it will crack (not that we have ever done that before).
- changes in color
- A change in the color of the concrete may indicate that the concrete was exposed to heat exceeding 550°F. Concrete exposed to temperatures above 550°F often turn a shade of pink which indicates that a chemical change has occurred in the iron-containing aggregates and cement paste.
- surface spalls
- High heat can cause the pore water in the concrete to evaporate which can lead to spalling of the concrete.
Our assessments also include testing of the concrete via a sounding hammer. A sounding hammer can be used to compare the resonance of the concrete after it is struck by the hammer. Healthy concrete will exhibit a sharp, high-frequency ringing sound when struck, while damaged or poor-quality concrete will typically exhibit a dull thud or soft noise.We, in corroboration with may documented cases, have found the sounding hammer technique to be a reliable and cost-effective means of assessing damage to concrete in the wake of a fire. The sounding hammer can also be used for destructive testing to assess the strength of the concrete. Healthy concrete will be unphased by a couple blows from a sounding hammer while heat-damaged concrete will crumble away with a few rigorous hits. Additionally the fracture mechanics of heat-damaged concrete is unique in that the fracture plane will typically form around the aggregate as opposed to directly through the aggregate, which is characteristic of healthy concrete.